The role of the flocculus of the monkey in saccadic eye movements.

1. Purkinje cell discharges were recorded from the flocculus of monkeys either spontaneously making saccadic eye movements (saccades) or trained to fixate a small visual target presented on a tangent screen. In the trained monkeys, saccades of known magnitude and direction were induced by changing the position of the fixation target. 2. Among 513 Purkinje cells, 343 units (66.9%) paused during saccades in all directions (286 units) or in particular directions (57 units). In most units, there were intimate temporal relationships between the beginnings of pauses and saccades, and between the ends of pasuses and saccades. 3. The pause in activity preceded saccades by an average of 9.6 msec, with a maximum lead time of 30 msec. In a fraction of the units (7.6%), the pause started after the onset of saccades. 4. There were 104 units (20.3%) which showed bursts during saccades in all directions (eighty-two units) or in particular directions (twenty-two units). 5. In sixty-six units (12.8%) a burst was associated with saccades in one direction and a pause in the opposite direction. 6. The burst in the burst and burst-pause units preceded saccades by an average of 3.8 msec. There was no significant difference in the lead times between these two groups of units. 7. There was a linear relationship between the duration of the pause in Purkinje cell activity and that of the accompanying saccade. A linear relationship was also seen between the pause duration and the magnitude of saccade.